The problem with "uncomprehensible" aliens is that we have a hard time identifying with them so Sci-fi writers refrain from writing them in unless they're represented as some sort of adversary with some dubious motives. That's actually the most common form of aliens that fit that category, since it gives the writers the freedom to create truly bizarre situations where aliens attack us, for no apparent reason, using tactics that don't make any sense and often creating borderline nonsensical situations without needing to explain them; why bother explaining what you can't comprehend?

Aliens playing supportive roles tend to be humanized so that we can relate to them, with few minor differences thrown in to give them endearing traits ("You humans are so weird doing X like that. On our world we do it like this."). Creating an alien that you're not supposed to be able to comprehend but the hero is constantly interacting with is incredibly hard to do and many writers simply don't want to bother working that hard to create a believable alien that the audience might not end up liking. That's why you don't see any Hanar in Shepard's crew.

Of course there are exception that can be found but they tend to fall outside the mainstream stuff. However most mainstream examples of uncomprehansable aliens tend to fall into the category of an adversary or occasionally as a mysterious forerunner/caretaker where the uncomprehensibility is used to excuse to not needing to explain their reasons. Real reasons behind that can be general laziness, the writer wants the focus of the story to be somewhere else or simply the cool factor.

I love all the aliens in Animorphs. The telepathic blue centaur men with no mouths who absorb nutrition from the grass with their hooves, the brain slugs who divide by fission and thus feel no connection to their young. Their society is built on treachery and backstabbing, but their completely without empathy. The Hork Bajiir, 8ft tall, heavily muscled scary looking aliens covered in blades..... that are used for cutting tree bark (their mind controlled into warriors but are actually hippy vegetarians!). Their usally quite dim (and designed that way) but theirs a genetic malfunction that causes every 100 of them or such to be born as a wise seer, and the taxons, ravenous blobs that are sentient but controlled by their own gnawing hunger.

And the powerful and eginmatic races who see beyond 3 dimensons and manipulate other races for good (the elimists) or evil (The Cyraks) .

This is something that I've always thought about too. Mass Effect was also the thing that got me thinking about it. The first game that is. The aliens just looked so unimaginative to me in that game, and then I slowly realised that these kind of human looking aliens are pretty much everywhere. And it's not just the human like aliens that disappoint me, it's more animalistic types too.

Like why do aliens have to have 4 limbs? Why do their limbs have to have the same number of joints as creatures from Earth? Why do their bodies have to be symmetrical? Why do they need to have a head? Why do their sensory organs have to be in the same place as animals from Earth? Why do they even have to have mouths and teeth? I can't think of any alien in fiction that actually looks truly alien. There's always some kind of familiarity which I think is unnecessary and somewhat unimaginative.

Although I do understand if you have aliens as actual characters in a story they have to look like humans so we can recognise and emote with them. But I still find it annoying that it's not more common for us to see aliens that actually look completely unfamiliar, whether they be characters in the story or merely native creatures.

That means two legs, two arms, one head, one body where all of these are attached to. And the legs are at the bottom, the arms are on the sides, the head is on top. You can elaborate with two eyes/ears, one mouth but that goes a bit out of scope. As long as it generally has human's body, it's humanoid. It doesn't matter if the face is really ugly or if it has the wrong number of fingers.

The yautja (the Predator race) exactly conform to humanoid specifications, down to having 5 fingers on their hands, two eyes and a single mouth (I'm not sure about ears but I'm willing to bet they have two as well. I think they also have 5 toes). And considering the Predators in the movies were played by an actual person in a suit, you cannot ever call them non-humanoid.

But one of the good thing they with the yautja was that they can see in different light spectrum. That is something too often forgot by sci-fi - not all races are able to see exactly the same things. Heck, even dogs see in a different light spectrum than humans, also hear different frequencies.

Wandering_Hero:I love all the aliens in Animorphs. The telepathic blue centaur men with no mouths who absorb nutrition from the grass with their hooves, the brain slugs who divide by fission and thus feel no connection to their young. Their society is built on treachery and backstabbing, but their completely without empathy. The Hork Bajiir, 8ft tall, heavily muscled scary looking aliens covered in blades..... that are used for cutting tree bark (their mind controlled into warriors but are actually hippy vegetarians!). Their usally quite dim (and designed that way) but theirs a genetic malfunction that causes every 100 of them or such to be born as a wise seer, and the taxons, ravenous blobs that are sentient but controlled by their own gnawing hunger.

And the powerful and eginmatic races who see beyond 3 dimensons and manipulate other races for good (the elimists) or evil (The Cyraks) .

Man... Animorphs was the shit

The many-armed, brightly colored slugs who painted the outsides of their spacecraft.

ZeroMachine:(WARNING: The following three are from Halo. Please, refrain from flaming me for bringing them up as examples. Regardless of your opinion on Halo, these ARE good examples.)

The Flood from Halo definitely come to mind.

And although they LOOK somewhat humanoid, I'd say the Forerunner are pretty damn alien because of their technology.

Also, the Lekgolo. They're the strange worms that make up the Hunters. The reason you come across paired Hunters most of the time is because they're both made up of a single colony of the worms.

Halo got my vote aswell. the flood and Lekgolo are quite alien, though why the lekgolo turn into bipedal things with 2 arms confuses me :s Surely out of all the things they can become, a bipedal humanoid creature is the most flawed.

ZeroMachine:(WARNING: The following three are from Halo. Please, refrain from flaming me for bringing them up as examples. Regardless of your opinion on Halo, these ARE good examples.)

The Flood from Halo definitely come to mind.

And although they LOOK somewhat humanoid, I'd say the Forerunner are pretty damn alien because of their technology.

Also, the Lekgolo. They're the strange worms that make up the Hunters. The reason you come across paired Hunters most of the time is because they're both made up of a single colony of the worms.

Halo got my vote aswell. the flood and Lekgolo are quite alien, though why the lekgolo turn into bipedal things with 2 arms confuses me :s Surely out of all the things they can become, a bipedal humanoid creature is the most flawed.

They did it for the sake of having relatively quick shock troopers, basically. And even in the games they aren't the only things the Lekgolo are used for. In Halo 3/ODST, the orange sinewy stuff around the Scarab cores are Lekgolo. V2 Scarabs are effectively gigantic Hunters.

Fieldy409:Ridley Scott's Alien is the first one that comes to mind. We never knew how smart they were for instance and how much of the creatures behavior was instinct.

I would say that every alien design in Alien feels genuinely... alien.

The derelict ship, the space jockey; All of them feel so far removed from our universe, you could easily imagine them originating from the farthest reaches of space. Which only added to the fear factor.

DANEgerous:Most Lovecraft monsters are exceptionally alien in both physiology and psychology.

Ugh, yeah. They are incomprehensible. So incomprehensible that the human mind tends to snap like a twig at the mere sight of some of them. For others almost any kind of knowledge can reduce a human to a gibbering wreck. All in all, trying to comprehend them tends to leave people either dead or horribly broken, so the task is impossible to complete.

That means two legs, two arms, one head, one body where all of these are attached to. And the legs are at the bottom, the arms are on the sides, the head is on top. You can elaborate with two eyes/ears, one mouth but that goes a bit out of scope. As long as it generally has human's body, it's humanoid. It doesn't matter if the face is really ugly or if it has the wrong number of fingers.

The yautja (the Predator race) exactly conform to humanoid specifications, down to having 5 fingers on their hands, two eyes and a single mouth (I'm not sure about ears but I'm willing to bet they have two as well. I think they also have 5 toes). And considering the Predators in the movies were played by an actual person in a suit, you cannot ever call them non-humanoid.

But one of the good thing they with the yautja was that they can see in different light spectrum. That is something too often forgot by sci-fi - not all races are able to see exactly the same things. Heck, even dogs see in a different light spectrum than humans, also hear different frequencies.

I know what a "humanoid" is, but I just figured it'd qualify (at least in this thread) seeing as it had the unusual mandibles and such, but you're correct, it's still humanoid.

I'll re-roll, I'll go with the Horta from the Star Trek universe. Not only are the Horta non-humanoid aliens, they're also of a completely different cellular structure seeing as they're a silicon based life form.

The trouble with trying to think of non-Earth creatures is that it's like trying to imagine a colour that's not in the spectrum.

I think the Combine from Half Life 2 are a good one. They assimilate technology and slaves from the planets they conquer. It was very odd to find out that the advisors are giant maggot-like creatures because you don't associate that with extreme intelligence.

Zack Alklazaris:The problem is can you think of a species that ISN'T bipedal that is as efficient as us? You can exactly picture a fish species making it to space travel.

What if the entire planet was underwater? Then a marine species might evolve limbs for tool use and become sapient. Eventually, they might make space ships filled with water, like giant flying fish tanks.

Scrustle:This is something that I've always thought about too. Mass Effect was also the thing that got me thinking about it. The first game that is. The aliens just looked so unimaginative to me in that game, and then I slowly realised that these kind of human looking aliens are pretty much everywhere. And it's not just the human like aliens that disappoint me, it's more animalistic types too.

Like why do aliens have to have 4 limbs? Why do their limbs have to have the same number of joints as creatures from Earth? Why do their bodies have to be symmetrical? Why do they need to have a head? Why do their sensory organs have to be in the same place as animals from Earth? Why do they even have to have mouths and teeth? I can't think of any alien in fiction that actually looks truly alien. There's always some kind of familiarity which I think is unnecessary and somewhat unimaginative.

Although I do understand if you have aliens as actual characters in a story they have to look like humans so we can recognise and emote with them. But I still find it annoying that it's not more common for us to see aliens that actually look completely unfamiliar, whether they be characters in the story or merely native creatures.

This was pretty much exactly what I was going after. Maybe the term "incomprehensible" was a bit too much, I admit. But it's not hard to come up with some rules that would make pretty freaky aliens. What if there were aliens whose home planet wasn't a ball, but, say, a tetrahedron? What if there was a planet whose mass would change during its solar cycle, and therefore gravity would change? A planet which was hollow and all life would be on the inside? A planet in the reaches of space where there would be no light (this was actually explored in a Green Lantern comic I once read)? Lifeforms not of solid matter, but for example, gas? The possibilities are out there, why does it seem that no one is grabbing them?